Previously known gravimeters, or accelerometers, utilizing capacitive pickups have been of the type which generally employ driving means responsive to a change in capacitive coupling to provide a null-restoring force to a pendulously-supported mass which includes one plate of a variable capacitor. The amount of feed-back current, as determined by the capacitor plate spacings due to movement of the mass, needed to restore the mass to a null position provides an indication of the momentary degree of variation from a level attitude in the device.
In most instances the recovery of a gravity-referenced null is the prime concern in such devices, the indication of degree of mislevel being for the most part axillary to that function of the device. Thus, such "restoring drive" devices have, at best, been capable of indicating a maximum momentary deviation from gravity null, yet have not provided a persistent signal of varying mislevel in any associated instrument. Further, it has been a consistent disadvantage of such mislevel-correcting devices that a significant amount of power is required, particularly in the restoring drive circuitry, in order to enable these instruments to complete their intended functions.
Other types of devices, more closely akin in function to the "spirit level", include a pendulously-supported core member which effects an inductive coupling in appropriate circuitry to generate an analog signal proportional to the degree of deviation of the instrument from a gravity-referenced level attitude. Again the power consumed in the operation of such an inductive pickup device, as well as the extensive circuitry required and unavoidable translation errors occasioned in analog-to-digital conversion, have further rendered these devices particularly unsuited to use in compact level-indicating instruments.
The present invention avoids the earlier disadvantages generally found in previously available instruments and provides a rugged, compact device which requires little power for operation and which provides, to a high degree of accuracy, a direct digital reading of conditions of gravity-related attitudes over a range of plus or minus 200 seconds of arc.